I recently noticed that whenever I do video playback the corresponding tab will spike to 60% CPU usage (in a single CPU thread) and doing profiler in Firefox's process manager clearly shows that Bitwarden (requestIdleCallback handler) causes this.
Disable the extension and refresh video website solves the issue for me.
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This issue can be mitigated by add domain name to Autofill setting -> Blocked domains
github.com bitwarden/client issue 12045